1. Field of the Invention
The present invention relates generally to locks, and, more particularly, concerns a lock assembly with an improved dead bolt cam configuration which permits the full extension or retraction of a dead bolt upon a 90.degree. rotation of the lock cylinder. Dead bolt lock assemblies of this type are commonly, but not exclusively, employed as drawer locks. The preliminary form of such a lock was disclosed in Disclosure Document No. 358,463, filed in the U.S. Patent and Trademark Office on Jul. 19, 1994.
2. Description of the Prior Art
Generally, drawer locks are comprised of a cylindrical lock plug which rotates within a lock housing and a dead bolt which moves linearly when the lock is rotated with a key. Located at the opposite end of the lock plug to where the key is inserted is a small cylindrical knob (cam) which fits into a slot cut within the dead bolt. When the lock plug is rotated within the lock housing, the cam moves within the dead bolt slot which, in turn, pushes the dead bolt along a channel formed on the lock housing and/or diamond shaped mounting flange. This interaction between the cam and the dead bolt slot provides the dead bolt with its linear back-and-forth motion.
Drawer locks customarily contain a dead bolt with a single slot oriented at a right angle to the direction of linear dead bolt travel (i.e. a non-angled slot). With this type of construction, 180.degree. of lock rotation is required to fully extend (lock) or retract (unlock) the dead bolt. Since 180.degree. of rotation is necessary to lock or unlock the drawer, the keyway slot will be at the same orientation (usually vertical) at both of these positions, which makes it virtually impossible for a user to visually determine whether the drawer is locked or not. This type of non-angled dead bolt slot fabrication is well known within the art.
Drawer locks also commonly have two or four equally spaced axial splines formed within the inner cylindrical contour of the lock housing which provide sites at which the key may be removed. When a properly fitted key is inserted into the lock plug, a tumbler mechanism within the lock is engaged and the tumblers become flush with the outer cylindrical contour of the lock plug which permits it to freely rotate within the inner cylindrical contour of the lock plug housing. The key, however, cannot be removed at non-spline locations because if it is partially extracted from the keyway entry, the tumblers disengage and spring load against the inner contour of the lock plug housing, which does not prevent subsequent lock rotation, but precludes any further extraction of the key. Yet, when the key is ultimately rotated to an orientation corresponding to a spline, the tumblers unload and fully release into the spline and the key may be removed, but any further rotation of the lock is obstructed by the contact between the disengaged tumblers and the spline. In sum, a key may not be removed at non-spline locations but may be freely withdrawn at any spline location, unless a spline filler insert is placed there. As a result, dual spline prior art drawer locks cannot incorporate a key retention feature at the unlocked position without the aid of a spline filler insert since both the locked and unlocked positions are oriented 180.degree. apart and coincide with spline locations.
Drawer locks also typically utilize lock plugs with disengageable retention mechanisms, usually a disk spring located near the opposite end of the lock plug to where the key is inserted, which, when engaged, seats upon a flange situated at the end of the inner contour of the lock plug housing. Such a mechanism holds the lock plug axially in place, but permits it to rotate within the lock plug housing.